Method and device for judging number of polarized branches of hybrid equivalent circuit of oil paper insulation equipment

Abstract

The invention provides a method and a device for judging the number of polarized branches of a hybrid equivalent circuit of oil-paper insulation equipment, and relates to the technical field of hybrid equivalent circuits, and the method comprises the following steps: obtaining a depolarization current curve of the oil-paper insulation equipment through testing, carrying out secondary differential on the depolarization current curve, and multiplying time to obtain a secondary differential time-domain spectral line of the depolarization current; and further analyzing the number of peak points of the spectral line and the abscissa parameter value of the spectral line so as to judge the number of RC series polarization branches and the number of RC series-parallel polarization branches in the series-parallel equivalent circuit. The method is simple, scientific and reasonable, can truly reflect the actual polarization branch number of the hybrid equivalent circuit of the oil-paper insulation equipment, and lays an important foundation for accurately evaluating the aging state of the insulating medium of the oil-paper insulation equipment based on equivalent circuit parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of series - parallel equivalent circuits, and particularly to a method and device for determining the number of polarization branches of a series - parallel equivalent circuit of an oil - paper insulation device. Background Art

[0002] In the power system, oil - paper insulation equipment is an important power transmission and conversion equipment, and the quality of its insulation performance is directly related to the safe operation and service life of the equipment. In order to evaluate the insulation state of oil - paper insulation equipment, especially the aging condition of its internal insulation medium, a series - parallel equivalent circuit model is widely used in related research. By simulating the electrical behavior of the insulation medium, this model can reflect the polarization characteristics of the oil - paper interface, thus providing a theoretical basis for aging state evaluation.

[0003] However, in practical applications, the accuracy of the series - parallel equivalent circuit model depends on the reasonable setting of the number of its polarization branches. Traditional methods usually assume the number of polarization branches of the series - parallel equivalent circuit based on experience, generally assuming 6 branches, including 4 series polarization branches and 2 series - parallel polarization branches. Although this assumption simplifies the model construction process to a certain extent, its limitations gradually become apparent when facing complex actual working conditions. During the long - term operation of oil - paper insulation equipment, it is affected by a variety of factors, such as temperature changes, electric field strength fluctuations, and moisture penetration. These factors will cause complex physical and chemical changes inside the insulation medium, generating aging products such as furfural and acids, and then changing the dielectric response characteristics of the insulation system. As the aging degree deepens, the complexity of the insulation medium increases continuously, and the traditionally assumed number of polarization branches cannot accurately reflect this dynamic change, resulting in limited reliability of the circuit parameters obtained based on this model and being difficult to truly reflect the actual aging state of the insulation system.

[0004] Therefore, the existing methods for setting the number of polarization branches of the series - parallel equivalent circuit cannot meet the need for accurately evaluating the aging state of oil - paper insulation equipment. There is an urgent need for a new method that can dynamically determine the number of polarization branches according to the actual aging situation to improve the scientificity and reliability of the series - parallel equivalent circuit model and provide a more accurate basis for the aging assessment of oil - paper insulation equipment.

[0005] In view of this, the present application is proposed. Summary of the Invention

[0006] The present invention provides a method and device for determining the number of polarization branches of a series - parallel equivalent circuit of an oil - paper insulation device, which can at least partially improve the above problems.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for determining the number of polarization branches of a series - parallel equivalent circuit of an oil - paper insulation device, which includes:

[0009] Measure the depolarization current in the parallel-series equivalent circuit of the oil-paper insulation equipment to be judged according to Kirchhoff's current law, and obtain the depolarization current curve;

[0010] Perform a second-order differential process on the depolarization current curve to obtain the second-order differential spectrum of the depolarization current, and multiply the second-order differential spectrum of the depolarization current by a preset time to obtain the second-order differential time-domain spectrum of the depolarization current;

[0011] Perform a logarithmic process on the second-order differential time-domain spectrum of the depolarization current, and judge the processed second-order differential time-domain spectrum of the depolarization current to generate a judgment result;

[0012] Based on a preset judgment rule and the judgment result, determine the number of polarization branches in the parallel-series equivalent circuit of the oil-paper insulation equipment.

[0013] The present invention also provides a device for judging the number of polarization branches in the parallel-series equivalent circuit of an oil-paper insulation equipment, which includes:

[0014] A current calculation unit for measuring the depolarization current in the parallel-series equivalent circuit of the oil-paper insulation equipment to be judged according to Kirchhoff's current law, and obtaining the depolarization current curve;

[0015] A second-order differential unit for performing a second-order differential process on the depolarization current curve to obtain the second-order differential spectrum of the depolarization current, and multiplying the second-order differential spectrum of the depolarization current by a preset time to obtain the second-order differential time-domain spectrum of the depolarization current;

[0016] A judgment unit for performing a logarithmic process on the second-order differential time-domain spectrum of the depolarization current, and judging the processed second-order differential time-domain spectrum of the depolarization current to generate a judgment result;

[0017] A quantity determination unit for determining the number of polarization branches in the parallel-series equivalent circuit of the oil-paper insulation equipment based on a preset judgment rule and the judgment result.

[0018] In summary, the innovation of the method for judging the number of polarization branches in the parallel-series equivalent circuit of the oil-paper insulation equipment lies in combining the time-domain characteristics of the depolarization current with the parameter identification of the parallel-series equivalent circuit, and excavating the polarization branch information hidden in the depolarization current through mathematical analysis; this method not only avoids the subjectivity of artificial assumptions, but also improves the scientificity and accuracy of parameter identification. This method breaks through the limitations of the traditional artificial assumption of the number of polarization branches, obtains the true depolarization current curve of the oil-paper insulation equipment through experimental testing, and combines mathematical analysis means to achieve accurate judgment of the number of different types of polarization branches in the parallel-series equivalent circuit. Description of the Drawings

[0019] Figure 1 It is a schematic flowchart of a method for determining the number of polarization branches of a hybrid equivalent circuit of an oil-paper insulation device provided in the first embodiment of the present invention;

[0020] Figure 2 It is a topological structure diagram of a hybrid equivalent circuit of an oil-paper insulation device provided in an embodiment of the present invention;

[0021] Figure 3 It is a superimposed diagram of secondary differential time-domain sub-spectrum lines of depolarization current provided in an embodiment of the present invention;

[0022] Figure 4 It is a secondary differential time-domain spectrum diagram of depolarization current provided in an embodiment of the present invention;

[0023] Figure 5 It is a module schematic diagram of a device for determining the number of polarization branches of a hybrid equivalent circuit of an oil-paper insulation device provided in the second embodiment of the present invention. Specific embodiments

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] Refer to Figure 1 As shown, the first embodiment of the present invention discloses a method for determining the number of polarization branches of a hybrid equivalent circuit of an oil-paper insulation device, which can be executed by an oil-paper insulation device hybrid equivalent circuit polarization branch number determination device (hereinafter referred to as the determination device), and particularly, by one or more processors in the determination device to implement the following method:

[0026] S1. According to Kirchhoff's current law, measure the depolarization current in the hybrid equivalent circuit of the oil-paper insulation device to be judged to obtain a depolarization current curve;

[0027] Please refer to Figure 2 , preferably, the hybrid equivalent circuit of the oil-paper insulation device includes a geometric polarization equivalent circuit and a polarization equivalent circuit;

[0028] The polarization equivalent circuit includes a series polarization equivalent circuit and a parallel-series polarization equivalent circuit. The geometric polarization equivalent circuit, the series polarization equivalent circuit and the parallel-series polarization equivalent circuit are connected in parallel. Among them, the geometric polarization equivalent circuit is composed of a parallel connection of an insulation resistance Rg and a geometric capacitance Cg. The series polarization equivalent circuit is composed of K RC series polarization branches connected in parallel. The parallel-series polarization equivalent circuit is composed of M RC parallel-series polarization branches connected in parallel. Both K and M are natural numbers;

[0029] Each of the RC series polarization branches includes a series polarization resistor and a series polarization capacitor, where the series polarization capacitor and the series polarization resistor are in series;

[0030] Each of the RC parallel - series polarization branches includes two parallel - series polarization resistors and a parallel - series polarization capacitor, where the second parallel - series polarization resistor is in parallel with the parallel - series polarization capacitor and then in series with the first parallel - series polarization resistor.

[0031] Specifically, step S1 includes: calculating the time constant of the series polarization capacitor on the i - th RC series polarization branch, and the calculation formula is: τ pi =R pi C pi where R pu is the value of the series polarization resistor on the i - th RC series polarization branch, C pu is the value of the series polarization capacitor on the i - th RC series polarization branch, and i = 1, 2,..., K;

[0032] Calculating the time constant of the parallel - series polarization capacitor on the j - th RC parallel - series polarization branch, and the calculation formula is: R h(2j) is the second parallel - series polarization resistor on the j - th RC parallel - series polarization branch, R h(2j-1) is the first parallel - series polarization resistor on the j - th RC parallel - series polarization branch, C hj is the parallel - series polarization capacitor on the j - th RC parallel - series polarization branch, and j = 1, 2,..., M;

[0033] According to Kirchhoff's current law, measure the depolarization current in the parallel - series equivalent circuit to obtain a depolarization current curve, where the depolarization current is the sum of the currents of each series polarization branch and parallel - series polarization branch;

[0034] The calculation formula is:

[0035]

[0036] where U 0 is the DC voltage source configured at both ends of the oil - paper insulated equipment, is an exponent related to the t c , τ pi parameters, is an exponential function with t as the variable, is an exponent related to the t c , τ hj parameters, is an exponential function with t as the variable, B i is the relaxation contribution coefficient of the i - th series polarization branch to the depolarization current, E jis the relaxation contribution coefficient of the j-th series-parallel polarization branch to the depolarization current.

[0037] In this embodiment, first, a series-parallel equivalent circuit model of the oil-paper insulation equipment is constructed. This model consists of a geometric polarization equivalent circuit and a polarization equivalent circuit. The geometric polarization equivalent circuit is formed by the parallel connection of an insulation resistance and a geometric capacitance, and is used to simulate the basic electrical characteristics of the insulating medium. The polarization equivalent circuit is further divided into a series polarization equivalent circuit and a series-parallel polarization equivalent circuit, which are used to simulate the polarization relaxation processes of insulating oil, the oil-paper interface, and insulating paper, respectively. The series polarization equivalent circuit is composed of K RC series polarization branches connected in parallel. Each branch contains a series polarization resistance and a series polarization capacitance, which are connected in series. The series-parallel polarization equivalent circuit is composed of M RC series-parallel polarization branches connected in parallel. Each branch contains two series-parallel polarization resistances and a series-parallel polarization capacitance, where the second series-parallel polarization resistance is connected in parallel with the series-parallel polarization capacitance and then connected in series with the first series-parallel polarization resistance.

[0038] Immediately afterwards, according to Kirchhoff's current law, the depolarization current in the series-parallel equivalent circuit is measured; the depolarization current is the sum of the currents of each series polarization branch and series-parallel polarization branch. When calculating specifically, for the i-th series polarization branch, its time constant is calculated; similarly, for the j-th series-parallel polarization branch, its time constant is also calculated. Based on the above time constants and Kirchhoff's current law, the depolarization current can be obtained.

[0039] Preferably, the time constants of the RC series polarization branches and the RC series-parallel polarization branches are used to represent the polarization relaxation rates of the corresponding insulating media. Among them, the small time constant branches in the RC series polarization branches correspond to the polarization relaxation process of insulating oil, the medium time constant branches in the RC series-parallel polarization branches correspond to the polarization relaxation process of the oil-paper interface, and the large time constant branches in the RC series polarization branches correspond to the polarization relaxation process of insulating paper. A small time constant means that the time constant is less than or equal to 1 s, a medium time constant means that the time constant is greater than 1 s and less than 100 s, and a large time constant means that the time constant is greater than or equal to 100 s.

[0040] In this embodiment, the above time constants not only reflect the electrical characteristics of each branch, but also are closely related to the polarization relaxation rate of the insulating medium. According to the magnitude of the time constant, the polarization relaxation process can be divided into three categories: small time constant branches (time constant less than or equal to 1 second) correspond to the polarization relaxation process of insulating oil; medium time constant branches (time constant greater than 1 second and less than 100 seconds) correspond to the polarization relaxation process of the oil-paper interface; large time constant branches (time constant greater than or equal to 100 seconds) correspond to the polarization relaxation process of insulating paper. This classification method can more accurately understand the polarization behavior of different insulating media during the aging process, thereby providing more abundant information for subsequent aging state assessment.

[0041] S2, perform a second - order differentiation on the depolarization current curve to obtain a second - order differential spectrum line of the depolarization current, and multiply the second - order differential spectrum line of the depolarization current by a preset time to obtain a second - order differential time - domain spectrum line of the depolarization current;

[0042] Specifically, step S2 includes: performing a second - order differentiation on the depolarization current curve to obtain a second - order differential spectrum line of the depolarization current

[0043] the second - order differential spectrum line of the depolarization current and a preset time t 2 perform a multiplication process to obtain a second - order differential time - domain spectrum line φ(t) of the depolarization current. The formula is:

[0044] where, is the i - th series - type sub - spectrum line of the second - order differential time - domain of the depolarization current, is the j - th parallel - series - type sub - spectrum line of the second - order differential time - domain of the depolarization current.

[0045] In this embodiment, further, performing a second - order differentiation on the depolarization current curve to obtain a second - order differential spectrum line of the depolarization current; the purpose of this processing step is to more clearly identify the characteristics of each polarization branch. Second - order differentiation is a mathematical processing method that can enhance the characteristics of small changes in the curve, making details that were originally difficult to detect more obvious. This method obtains a second - order differential spectrum line by performing a second - order differentiation on the depolarization current; to more clearly identify the characteristics of each polarization branch because second - order differentiation can highlight the peaks and inflection points in the curve, and these characteristics are closely related to the number of polarization branches. Immediately afterwards, to further enhance the recognizability of the characteristics, multiply the second - order differential spectrum line by a preset time to obtain a second - order differential time - domain spectrum line of the depolarization current; the purpose of this multiplication process is to amplify the key characteristics in the spectrum line, making the peak points more obvious.

[0046] In this embodiment, through mathematical analysis of the i - th series - type sub - spectrum line, it can be known that it has a unique peak point, and rapidly decays to 0 on both sides, and the abscissa of its peak point is 2τ pi ; Similarly, through mathematical analysis of the j - th parallel - series - type sub - spectrum line, it can be known that it has a unique peak point, and rapidly decays to 0 on both sides, and the abscissa of its peak point is 2τ hj . To further study the characteristics of the second - order differential time - domain spectrum line of the depolarization current with multiple sub - spectrum lines superimposed, four different time constants are selected (τ 1 = 28.75, τ 2 = 3.31, τ 3 = 0.46, τ4 sub - spectral lines (with τ = 0.06), corresponding to sub - spectral line 1, sub - spectral line 2, sub - spectral line 3, and sub - spectral line 4 respectively; the second - order differential time - domain spectral lines formed by their superposition are studied, and the superposition situation is as Figure 3 shown.

[0047] Specifically, according to Figure 3 it can be known that the second - order differential time - domain spectral lines of the depolarization current have the following characteristics: the second - order differential time - domain spectral lines of the depolarization current have obvious peak points, and the number of peak points is equal to the number of sub - spectral lines; the sub - spectral lines inside the second - order differential time - domain spectral lines of the depolarization current have a unique peak point and rapidly decay to 0 on both sides; the abscissa of the peak point of the series - type sub - spectral line is 2τ pi , and the number K of series - type sub - spectral lines can be determined according to the abscissa parameter values of each peak point; the abscissa of the peak point of the series - parallel type sub - spectral line is 2τ hj , and the number M of series - parallel type sub - spectral lines can be determined according to the abscissa parameter values of each peak point.

[0048] S3. Take the logarithm of the second - order differential time - domain spectral lines of the depolarization current, and make a determination on the processed second - order differential time - domain spectral lines of the depolarization current to generate a determination result;

[0049] Specifically, step S3 includes: taking the logarithm of both the abscissa and ordinate of the second - order differential time - domain spectral lines of the depolarization current to make the peak points of the second - order differential time - domain spectral lines of the depolarization current clear;

[0050] Determine the number N1 of peak points of the second - order differential time - domain spectral lines of the depolarization current within the first preset range and the second preset range;

[0051] Determine the number N2 of peak points of the second - order differential time - domain spectral lines of the depolarization current within the third preset range;

[0052] Generate a determination result according to the number N1 of peak points and the number N2 of peak points.

[0053] Preferably, the first preset range is t ≥ 200 s, the second preset time range is t ≤ 2 s, and the third preset time range is 2 s < t < 200 s.

[0054] S4. Based on the preset determination rule and the determination result, determine the number of polarization branches in the series - parallel equivalent circuit of the oil - paper insulation equipment.

[0055] Specifically, step S4 includes: the determination rule is that the number of peak points of the second - order differential time - domain spectral lines of the depolarization current within the first preset range and the second preset range is the total number K of RC series - connected polarization branches, and the number of peak points of the second - order differential time - domain spectral lines of the depolarization current within the third preset range is the total number M of RC series - parallel polarization branches.

[0056] In this embodiment, according to the characteristics of the second differential time-domain spectrum of the depolarization current, further analyze the number of peak points of each sub-spectrum line of the second differential time-domain spectrum of the depolarization current, and determine the number of polarization branches corresponding to each type of the series-parallel equivalent circuit based on the internal relationship between the abscissa parameter value of the sub-spectrum line and the time constant of the corresponding polarization branch.

[0057] By analyzing the second differential time-domain spectrum of the depolarization current, obvious peak points can be observed. The number and position of these peak points are closely related to the number of polarization branches. Specifically, the number of peak points of the second differential time-domain spectrum of the depolarization current in the first preset range and the second preset range corresponds to the number K of RC series polarization branches, while the number of peak points in the third preset range corresponds to the number M of RC series-parallel polarization branches. The beneficial effect of this method is that it can not only accurately determine the number of polarization branches, but also distinguish the polarization relaxation processes of different insulating media through the classification of time constants. This enables us to understand the internal state of oil-paper insulation equipment at different aging stages more deeply, thus providing more powerful support for the accurate assessment of the aging state.

[0058] Specifically, in order to make the peak points of the spectrum clearer, the abscissa and ordinate of the second differential time-domain spectrum of the depolarization current are logarithmically processed simultaneously. The logarithmic processing can effectively compress the data range, making the peak points in the spectrum more prominent and facilitating subsequent analysis. Through the logarithmic processing, the processed second differential time-domain spectrum of the depolarization current can be obtained. The beneficial effect of this processing step is that it can significantly improve the visibility of weak signals in the spectrum, making the peak points that were originally difficult to distinguish become more obvious, thereby improving the accuracy of the determination.

[0059] Next, first determine the number of peak points of the second differential time-domain spectrum of the depolarization current in the first preset range, and then determine the number of peak points of the second differential time-domain spectrum of the depolarization current in the third preset range; and according to the determination rule, the numbers of RC series polarization branches and RC series-parallel polarization branches are determined. The proposal of this determination rule enables the number of polarization branches to be directly determined through mathematical analysis, avoiding the subjectivity of artificial assumptions in traditional methods and improving the scientificity and accuracy of parameter identification.

[0060] Specifically, in this embodiment, in order to further reflect the accuracy of the method for determining the number of polarization branches of the series-parallel equivalent circuit of the oil-paper insulation equipment, here a verification is carried out on the series-parallel equivalent circuit of a actually operating transformer T1. The parameters of the series-parallel equivalent circuit of transformer T1 are shown in Table 1. Based on the data in Table 1 and in combination with this method, the second differential time-domain spectrum of transformer T1 (with an externally applied charging voltage set at 2 kV and a charging time of 5000 s) is constructed, and its graph is as Figure 4 shown.

[0061] Table 1 Transformer T1 parallel-parallel equivalent circuit parameters

[0062]

[0063] Depend on Figure 4 It can be seen that the number of peak points of the second differential time-domain spectrum of the depolarization current in the two ranges of t ≥ 200s and t ≤ 2s are 2 and 2 respectively; <t<200s范围内的峰值点个数为2个。所以根据本方法所提的极化支路数判定定则,可以判定变压器T1混联等效电路含有2条τ≤1s的串联极化支路、2条τ≥100s的串联极化支路、2条1s<τ<100s的混联极化支路。该结论与变压器T1实际的混联等效电路各类极化支路数一致,验证了混联等效电路极化支路数判定方法的可靠性与准确性。

[0064] In summary, the method for determining the number of polarization branches in the hybrid equivalent circuit of oil-paper insulation equipment uses the number of peak points of the secondary differential time-domain spectrum of the depolarization current to determine the number of various types of polarization branches inside the hybrid equivalent circuit of oil-paper insulation equipment. It uses mathematical methods to mine the real number of hybrid equivalent circuit branches hidden inside the depolarization current of oil-paper insulation equipment. The beneficial effect of this method is that it can not only dynamically reflect the aging state of the insulation equipment, but also provide a scientific basis for subsequent aging evaluation. Through experimental verification, this method can accurately determine the number of polarization branches in the hybrid equivalent circuit of the actual operating transformer, which is consistent with the actual circuit parameters, verifying the accuracy and reliability of the method. In addition, this method avoids the subjectivity of traditional artificial assumptions, improves the scientificity and accuracy of parameter identification, and provides a new and effective technical means for the aging state monitoring and evaluation of oil-paper insulation equipment.

[0065] In short, the method for determining the number of polarization branches of the parallel-parallel equivalent circuit of oil-paper insulation equipment is not only innovative in theory, but also has important value in practical applications. Through this method, the insulation state of oil-paper insulation equipment can be more accurately evaluated, and potential aging problems can be discovered in time, thereby providing a strong guarantee for the safe operation of the power system. This method is simple and easy to implement, has high scientificity and practicality, is suitable for aging state monitoring and evaluation of various oil-paper insulation equipment, and has broad application prospects.

[0066] See also Figure 5 The second embodiment of the present invention provides a device for determining the number of polarization branches of a parallel-parallel equivalent circuit of an oil-paper insulation device, which comprises:

[0067] The current calculation unit 101 is used to obtain the depolarization current in the parallel-parallel equivalent circuit of the oil-paper insulation device to be judged according to Kirchhoff's current law test, and obtain the depolarization current curve;

[0068] The second differential unit 102 is configured to perform a second differential process on the depolarization current curve to obtain a second differential spectrum of the depolarization current, and multiply the second differential spectrum of the depolarization current by a preset time to obtain a second differential time-domain spectrum of the depolarization current;

[0069] The determination unit 103 is configured to perform a logarithm-taking process on the second differential time-domain spectrum of the depolarization current, and determine the processed second differential time-domain spectrum of the depolarization current to generate a determination result;

[0070] The quantity determination unit 104 is configured to determine the number of polarization branches in the parallel-series equivalent circuit of the oil-paper insulation equipment based on a preset determination rule and the determination result.

[0071] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A method for determining the number of polarization branches in a parallel-parallel equivalent circuit of oil-paper insulated equipment, characterized in that: include: According to Kirchhoff's current law test, the depolarization current in the parallel-parallel equivalent circuit of the oil-paper insulation equipment to be judged is obtained, and the depolarization current curve is obtained; Performing secondary differential processing on the depolarization current curve to obtain a secondary differential spectrum of the depolarization current, and multiplying the secondary differential spectrum of the depolarization current by a preset time to obtain a secondary differential time-domain spectrum of the depolarization current; Performing logarithmic processing on the second differential time-domain spectrum line of the depolarization current, and judging the second differential time-domain spectrum line of the depolarization current after the processing to generate a judgment result; Based on the preset judgment rule and the judgment result, the number of polarization branches in the parallel-parallel equivalent circuit of the oil-paper insulation equipment is determined.

2. The method for determining the number of polarization branches of a parallel-parallel equivalent circuit of oil-paper insulated equipment according to claim 1, characterized in that: The parallel-parallel equivalent circuit of the oil-paper insulation equipment includes a geometric polarization equivalent circuit and a polarization equivalent circuit; The polarization equivalent circuit includes a series polarization equivalent circuit and a parallel-parallel polarization equivalent circuit. The geometric polarization equivalent circuit, the series polarization equivalent circuit and the parallel-parallel polarization equivalent circuit are connected in parallel. The geometric polarization equivalent circuit is composed of an insulation resistance R g and geometric capacitance C g The series polarization equivalent circuit is composed of K RC series polarization branches connected in parallel, and the hybrid polarization equivalent circuit is composed of M RC hybrid polarization branches connected in parallel, where K and M are both natural numbers; Each of the RC series polarization branches includes a series polarization resistor and a series polarization capacitor, wherein the series polarization capacitor and the series polarization resistor are connected in series; Each of the RC hybrid polarization branches includes two hybrid polarization resistors and one hybrid polarization capacitor, wherein the second hybrid polarization resistor is connected in parallel with the hybrid polarization capacitor and then connected in series with the first hybrid polarization resistor.

3. The method for determining the number of polarization branches of a parallel-parallel equivalent circuit of oil-paper insulated equipment according to claim 2, characterized in that: According to Kirchhoff's current law test, the depolarization current in the parallel-parallel equivalent circuit of the oil-paper insulation equipment to be judged is obtained, and the depolarization current curve is obtained, which is specifically: Calculate the time constant of the series polarized capacitor on the i-th RC series polarized branch. The calculation formula is: τ pi =R pi C pi , where R pi is the series polarization resistance value of the i-th RC series polarization branch, C pi is the series polarization capacitance value of the i-th RC series polarization branch, i=1,2,...,K; Calculate the time constant of the hybrid polarization capacitor on the jth RC hybrid polarization branch. The calculation formula is: R h(2j) is the second parallel-connection polarization resistor on the jth RC parallel-connection polarization branch, R h(2j-1) is the first hybrid polarization resistor on the jth RC hybrid polarization branch, C hj is the hybrid polarization capacitor on the jth RC hybrid polarization branch, j = 1, 2, ..., M; According to Kirchhoff's current law, the depolarization current in the parallel-parallel equivalent circuit is tested and obtained to obtain a depolarization current curve, wherein the depolarization current is the sum of the currents of each series polarization branch and the parallel-parallel polarization branch; The calculation formula is: Among them, U0 is the DC voltage source configured at both ends of the oil-paper insulation equipment, For c , τ pi Parameters related to the index, is an exponential function with t as the variable, For c , τ hj Parameters related to the index, is an exponential function with t as the variable, B u is the relaxation contribution coefficient of the ith series polarization branch to the depolarization current, E j is the relaxation contribution coefficient of the jth hybrid polarization branch to the depolarization current.

4. The method for determining the number of polarization branches of a parallel-parallel equivalent circuit of oil-paper insulated equipment according to claim 2, characterized in that: The time constant of the RC series polarization branch and the time constant of the RC hybrid polarization branch are used to represent the polarization relaxation rate of the corresponding insulating medium, wherein the small time constant branch in the RC series polarization branch corresponds to the polarization relaxation process of the insulating oil, the medium time constant branch in the RC hybrid polarization branch corresponds to the polarization relaxation process of the oil-paper interface, and the large time constant branch in the RC series polarization branch corresponds to the polarization relaxation process of the insulating paper. The small time constant indicates that the time constant is less than or equal to 1s, the medium time constant indicates that the time constant is greater than 1s and less than 100s, and the large time constant indicates that the time constant is greater than or equal to 100s.

5. The method for determining the number of polarization branches of a parallel-parallel equivalent circuit of oil-paper insulated equipment according to claim 4, characterized in that: The depolarization current curve is subjected to secondary differential processing to obtain a depolarization current secondary differential spectrum line, and the depolarization current secondary differential spectrum line is multiplied by a preset time to obtain a depolarization current secondary differential time domain spectrum line, specifically: The depolarization current curve is subjected to secondary differential processing to obtain the depolarization current secondary differential spectrum line The second differential spectrum of the depolarization current With the preset time t 2 Perform product processing to obtain the second differential time domain spectrum of the depolarization current The formula is: in, is the ith depolarization current second-order differential time-domain series sub-spectrum line, It is the jth depolarization current secondary differential time domain mixed sub-spectrum line.

6. The method for determining the number of polarization branches of a parallel-parallel equivalent circuit of oil-paper insulated equipment according to claim 1, characterized in that: The depolarization current second differential time domain spectrum line is logarithmically processed, and the processed depolarization current second differential time domain spectrum line is judged to generate a judgment result, which is specifically: Performing logarithmic processing on the horizontal and vertical coordinates of the second differential time-domain spectrum line of the depolarization current, so as to make the peak point of the second differential time-domain spectrum line of the depolarization current clear; Determine the number N1 of peak points of the second differential time-domain spectrum of the depolarization current within the first preset range and the second preset range; Determine the number N2 of peak points of the second differential time-domain spectrum of the depolarization current within a third preset range; A determination result is generated according to the number of peak points N1 and the number of peak points N2.

7. The method for determining the number of polarization branches of a parallel-parallel equivalent circuit of oil-paper insulated equipment according to claim 6, characterized in that: The first preset time range is t≥200s, the second preset time range is t≤2s, and the third preset time range is 2s. <t<200s。 8. The method for determining the number of polarization branches of a parallel-parallel equivalent circuit of oil-paper insulated equipment according to claim 6, characterized in that: The determination rule is that the number of peak points of the second differential time domain spectrum of the depolarization current within the first preset range and the second preset range is the total number K of RC series polarization branches, and the number of peak points of the second differential time domain spectrum of the depolarization current within the third preset range is the total number M of RC hybrid polarization branches.

9. A device for determining the number of polarization branches in a parallel-parallel equivalent circuit of oil-paper insulated equipment, characterized in that: include: A current calculation unit, used to test and obtain the depolarization current in the parallel-parallel equivalent circuit of the oil-paper insulation device to be judged according to Kirchhoff's current law, and obtain a depolarization current curve; A secondary differential unit, used for performing secondary differential processing on the depolarization current curve to obtain a secondary differential spectrum of the depolarization current, and multiplying the secondary differential spectrum of the depolarization current by a preset time to obtain a secondary differential time-domain spectrum of the depolarization current; A determination unit, configured to perform logarithmic processing on the depolarization current second differential time domain spectrum line, and determine the processed depolarization current second differential time domain spectrum line to generate a determination result; The quantity determination unit is used to determine the number of polarization branches in the parallel-parallel equivalent circuit of the oil-paper insulation equipment based on a preset determination rule and the determination result.

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